lecture 13 Flashcards
(23 cards)
motor system organization
basal ganglia: gating proper initiation of movement descending system: motor cortex/brainstem
- planning initiating and directing voluntary movement
spinal cord and brainstem: local circuit neutrons and motor neurone pools
sensory input/motor output (skeletal muscle)
basal ganglia function
suppresses unwanted movements, prepares upper MN circuits for movement initiation
cerebellum function
sensory motor coordination of ongoing movement
- detects and attenuates error signals
dorsal/ ventral motor regions
cerebral cortex–> lateral ventral horn (distal limb)
brainstem–> medial ventral horn (posture/balance)
ventral = motor, dorsal = sensory
lower motor neurons
LMN - send axons out of brainstem and spinal cord to innervate skeletal muscles of head (bstem) and body (spinal cord)
local circuit neurons
innervate the lower motor neurone and receive input from upper motor neuron and sensory input
primary motor cortex and pre motor cortex
planning initiation and directing sequences of movements
motor pools vs motor units
motor pool: nnervate an entire muscle
motor unit: motor neuron and the muscle fiber that it innervates
vertebrate nmj
polyinervated to mono neuronal - end plate with active zones but only one motor neuron per fibre
- during maturation they innervate multiple muscle fibres at the same place and fight for territory based on pre synaptic activity - more active one wins
motor unit summation
contractions dissipate between action potentials
start to summate around 10-20Hz but become fused at 50- 80Hz (tetanus)
contraction strength
due to increased firing rate of motor neurons AND recruitment of additional motor units
fatiguing of MNs
slow: small, contract slow, lots of mitochondria, resistant to fatigue
fast: large MN, largest muscle fiber, few mitochondria
Fast fatigue resistant- medium sized, less prone to fatigue
local circuit neurons
short distance: lateral and don’t have collaterals to contralateral side (final control of distal)
medial long distance: local circuit neurone have long axons with contralateral collaterals to help coordinate left and right sides (posture control)
reflex loops
hitting knee stretches tendon involuntarily and system tries to keep steady leg position by using extensor muscle
activation of 1 muscle and inhibition of antagonistic muscle
muscle spindle (aMN, yMN, Ia afferent)
sensory afferents synapse with aMNs for same and complementary muscles- also with inhibitory MN of antagonistic yMN adjust length of intrafusal fibres to maintain tension on sensory afferents sensory afferents (Ia) stretch receptors detect length of intrafusal
stretch reflex circuitry
descending facilitation and inhibition –> a motor neurone –> muscle –> load –> length change in muscle fibre –> spindle receptor –> a motor neuron
muscle spindle length regulation
extrafusal contraction slacks intrafusal fibres and they are not able to detect stretch - Y MN contract intrafusal fibres and allow length to be restored
length regulation of intrafusal fibers of Golgi tendon organ
in series with extrafusal fibres, muscle contraction increases with afferent activity
Golgi tendon organ (1b afferent)
1b afferent inhibits the same muscle that creates tension with inhibitory interneurons and excite antagonistic muscle
decrease muscle activity if too much tension builds
paralysis, paresis arflexia
paralysis- loss of movement
paresis - weakness
arflexia - loss of spinal reflexes
caused by damage to lower motor neurons in spinal cord
muscle tone
result of resting level of firing alpha motor neurons
muscle spindle afferents
hypo/hyper tonia
hypotonia- damage to lower MN or spindle afferents
hypertonia - damage to descending pathways (upper MN to spinal cord) causes chronic contraction and no stretch
central pattern generators
activated by proprioceptive inputs (muscle stretch)
can activate in a a cat by dragging feet back even in the absence of descending control
